336 Object-Based Programming Chapter 8 SUMMARY Every (Hp web site)
336 Object-Based Programming Chapter 8 SUMMARY Every class in C# inherits directly or indirectly from class Object. Keywords publicand private are member access modifiers. Instance variables and methods that are declared with member access modifier public are accessible wherever the program has a reference to an object of that class. Instance variables and methods that are declared with member access modifier private are accessible only to non-staticmethods of the class in which the private members are defined. The privatemethods often are called utility methods, or helper methods, because they can be called only by other methods of that class and are used to support the operation of those methods. Access methods can read or display data. Another common use for access methods is to test the truth of conditions such methods often are called predicate methods. A constructor initializes the instance variables of a class object. A class s constructor is called automatically when an object of that class is instantiated. It is common to have overloaded constructors for a class. Normally, constructors are public. Every class in C#, such as the classes from the .NET Framework, belongs to a namespace. If the programmer does not specify the namespace for a class, the class is placed in the default namespace, which includes the compiled classes in the current directory. Instance variables can be initialized by the class constructor, or they can be assigned values by the set accessor of a property. Instance variables that are not initialized explicitly by the programmer are initialized by the compiler (primitive numeric variables are set to 0, bool values are set to false and references are set to null). Classes simplify programming, because the client code need only be concerned with the public operations encapsulated in an object of the class. A class s non-static instance variables and methods belong to that class s scope. Within a class s scope, class members are immediately accessible to all of that class s non-static methods and can be referenced simply by name. Outside a class s scope, class members cannot be referenced directly by name. Variables defined in a method are known only to that method (i.e., they are local to that method). Such variables are said to have block scope. If a method defines a variable that has the same name as a variable with class scope, the class- scope variable is hidden by the block-scope variable in that method. To allow clients to manipulate the value of private data, the class can provide a property definition, which will enable the user to access this privatedata in a safe way. A property definition contains accessor methods that handle the details of modifying and returning data. A property definition can contain a set accessor, a get accessor or both. A get accessor enables the client to read the field s value and the setaccessor enables the client to modify the value. When an object is created, its members can be initialized by a constructor of that object s class. If no constructors are defined for a class, a default constructor will be provided by the compiler. This constructor contains no code and takes no parameters. Methods and constructors of a class can be overloaded. To overload a method of a class, simply provide a separate method definition with the same name for each version of the method. Remember that overloaded methods/constructors must have different parameter lists.
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